diff --git a/src/backuptask.js b/src/backuptask.js
index 0cdff58d5..791b86abb 100644
--- a/src/backuptask.js
+++ b/src/backuptask.js
@@ -418,36 +418,35 @@ function upload(remotePath, format, dataLayoutString, progressCallback, callback
 
     const dataLayout = DataLayout.fromString(dataLayoutString);
 
-    getBackupConfig(function (error, backupConfig) {
+    getBackupConfig(async function (error, backupConfig) {
         if (error) return callback(error);
 
-        storage.api(backupConfig.provider).checkPreconditions(backupConfig, dataLayout, function (error) {
-            if (error) return callback(error);
+        const [preconditionError] = await safe(storage.api(backupConfig.provider).checkPreconditions(backupConfig, dataLayout));
+        if (preconditionError) return callback(preconditionError);
 
-            if (format === 'tgz') {
-                async.retry({ times: 5, interval: 20000 }, function (retryCallback) {
-                    retryCallback = once(retryCallback); // protect again upload() erroring much later after tar stream error
+        if (format === 'tgz') {
+            async.retry({ times: 5, interval: 20000 }, function (retryCallback) {
+                retryCallback = once(retryCallback); // protect again upload() erroring much later after tar stream error
 
-                    tarPack(dataLayout, backupConfig.encryption, function (error, tarStream) {
-                        if (error) return retryCallback(error);
+                tarPack(dataLayout, backupConfig.encryption, function (error, tarStream) {
+                    if (error) return retryCallback(error);
 
-                        tarStream.on('progress', function (progress) {
-                            const transferred = Math.round(progress.transferred/1024/1024), speed = Math.round(progress.speed/1024/1024);
-                            if (!transferred && !speed) return progressCallback({ message: 'Uploading backup' }); // 0M@0MBps looks wrong
-                            progressCallback({ message: `Uploading backup ${transferred}M@${speed}MBps` });
-                        });
-                        tarStream.on('error', retryCallback); // already returns BoxError
-
-                        storage.api(backupConfig.provider).upload(backupConfig, storage.getBackupFilePath(backupConfig, remotePath, format), tarStream, retryCallback);
+                    tarStream.on('progress', function (progress) {
+                        const transferred = Math.round(progress.transferred/1024/1024), speed = Math.round(progress.speed/1024/1024);
+                        if (!transferred && !speed) return progressCallback({ message: 'Uploading backup' }); // 0M@0MBps looks wrong
+                        progressCallback({ message: `Uploading backup ${transferred}M@${speed}MBps` });
                     });
-                }, callback);
-            } else {
-                async.series([
-                    saveFsMetadata.bind(null, dataLayout, `${dataLayout.localRoot()}/fsmetadata.json`),
-                    sync.bind(null, backupConfig, remotePath, dataLayout, progressCallback)
-                ], callback);
-            }
-        });
+                    tarStream.on('error', retryCallback); // already returns BoxError
+
+                    storage.api(backupConfig.provider).upload(backupConfig, storage.getBackupFilePath(backupConfig, remotePath, format), tarStream, retryCallback);
+                });
+            }, callback);
+        } else {
+            async.series([
+                saveFsMetadata.bind(null, dataLayout, `${dataLayout.localRoot()}/fsmetadata.json`),
+                sync.bind(null, backupConfig, remotePath, dataLayout, progressCallback)
+            ], callback);
+        }
     });
 }
 
diff --git a/src/storage/filesystem.js b/src/storage/filesystem.js
index 637dce44d..3d25de419 100644
--- a/src/storage/filesystem.js
+++ b/src/storage/filesystem.js
@@ -63,35 +63,32 @@ function getRootPath(apiConfig) {
 }
 
 // the du call in the function below requires root
-async function checkPreconditions(apiConfig, dataLayout, callback) {
+async function checkPreconditions(apiConfig, dataLayout) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert(dataLayout instanceof DataLayout, 'dataLayout must be a DataLayout');
-    assert.strictEqual(typeof callback, 'function');
 
     let used = 0;
     for (let localPath of dataLayout.localPaths()) {
         debug(`checkPreconditions: getting disk usage of ${localPath}`);
         let result = safe.child_process.execSync(`du -Dsb ${localPath}`, { encoding: 'utf8' });
-        if (!result) return callback(new BoxError(BoxError.FS_ERROR, `du error: ${safe.error.message}`));
+        if (!result) throw new BoxError(BoxError.FS_ERROR, `du error: ${safe.error.message}`);
         used += parseInt(result, 10);
     }
 
     debug(`checkPreconditions: ${used} bytes`);
 
     const [error, result] = await safe(df.file(getRootPath(apiConfig)));
-    if (error) return callback(new BoxError(BoxError.FS_ERROR, `Error when checking for disk space: ${error.message}`));
+    if (error) throw new BoxError(BoxError.FS_ERROR, `Error when checking for disk space: ${error.message}`);
 
     // Check filesystem is mounted so we don't write into the actual folder on disk
     if (apiConfig.provider === PROVIDER_SSHFS || apiConfig.provider === PROVIDER_CIFS || apiConfig.provider === PROVIDER_NFS || apiConfig.provider === PROVIDER_EXT4) {
-        if (result.mountpoint !== paths.MANAGED_BACKUP_MOUNT_DIR) return callback(new BoxError(BoxError.FS_ERROR, 'Backup target is not mounted'));
+        if (result.mountpoint !== paths.MANAGED_BACKUP_MOUNT_DIR) throw new BoxError(BoxError.FS_ERROR, 'Backup target is not mounted');
     } else if (apiConfig.provider === PROVIDER_MOUNTPOINT) {
-        if (result.mountpoint === '/') return callback(new BoxError(BoxError.FS_ERROR, `${apiConfig.backupFolder} is not mounted`));
+        if (result.mountpoint === '/') throw new BoxError(BoxError.FS_ERROR, `${apiConfig.backupFolder} is not mounted`);
     }
 
     const needed = 0.6 * used + (1024 * 1024 * 1024); // check if there is atleast 1GB left afterwards. aim for 60% because rsync/tgz won't need full 100%
-    if (result.available <= needed) return callback(new BoxError(BoxError.FS_ERROR, `Not enough disk space for backup. Needed: ${prettyBytes(needed)} Available: ${prettyBytes(result.available)}`));
-
-    callback(null);
+    if (result.available <= needed) throw new BoxError(BoxError.FS_ERROR, `Not enough disk space for backup. Needed: ${prettyBytes(needed)} Available: ${prettyBytes(result.available)}`);
 }
 
 function hasChownSupportSync(apiConfig) {
diff --git a/src/storage/gcs.js b/src/storage/gcs.js
index 462eb122c..d66cc1773 100644
--- a/src/storage/gcs.js
+++ b/src/storage/gcs.js
@@ -70,12 +70,9 @@ function getRootPath(apiConfig) {
     return apiConfig.prefix;
 }
 
-function checkPreconditions(apiConfig, dataLayout, callback) {
+async function checkPreconditions(apiConfig, dataLayout) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert(dataLayout instanceof DataLayout, 'dataLayout must be a DataLayout');
-    assert.strictEqual(typeof callback, 'function');
-
-    callback(null);
 }
 
 function upload(apiConfig, backupFilePath, sourceStream, callback) {
diff --git a/src/storage/interface.js b/src/storage/interface.js
index 353f5b30b..8bb9949d0 100644
--- a/src/storage/interface.js
+++ b/src/storage/interface.js
@@ -34,7 +34,7 @@ exports = module.exports = {
     injectPrivateFields
 };
 
-var assert = require('assert'),
+const assert = require('assert'),
     BoxError = require('../boxerror.js'),
     DataLayout = require('../datalayout.js'),
     EventEmitter = require('events');
@@ -56,12 +56,9 @@ function getRootPath(apiConfig) {
     return '/';
 }
 
-function checkPreconditions(apiConfig, dataLayout, callback) {
+async function checkPreconditions(apiConfig, dataLayout) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert(dataLayout instanceof DataLayout, 'dataLayout must be a DataLayout');
-    assert.strictEqual(typeof callback, 'function');
-
-    callback(null);
 }
 
 function upload(apiConfig, backupFilePath, sourceStream, callback) {
diff --git a/src/storage/noop.js b/src/storage/noop.js
index d3a10ca82..772d2b1d5 100644
--- a/src/storage/noop.js
+++ b/src/storage/noop.js
@@ -22,7 +22,7 @@ exports = module.exports = {
     injectPrivateFields
 };
 
-var assert = require('assert'),
+const assert = require('assert'),
     BoxError = require('../boxerror.js'),
     DataLayout = require('../datalayout.js'),
     debug = require('debug')('box:storage/noop'),
@@ -33,12 +33,9 @@ function getRootPath(apiConfig) {
     return '';
 }
 
-function checkPreconditions(apiConfig, dataLayout, callback) {
+async function checkPreconditions(apiConfig, dataLayout) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert(dataLayout instanceof DataLayout, 'dataLayout must be a DataLayout');
-    assert.strictEqual(typeof callback, 'function');
-
-    callback(null);
 }
 
 function upload(apiConfig, backupFilePath, sourceStream, callback) {
diff --git a/src/storage/s3.js b/src/storage/s3.js
index fa2e3fac2..7f953c0be 100644
--- a/src/storage/s3.js
+++ b/src/storage/s3.js
@@ -98,12 +98,9 @@ function getRootPath(apiConfig) {
     return apiConfig.prefix;
 }
 
-function checkPreconditions(apiConfig, dataLayout, callback) {
+async function checkPreconditions(apiConfig, dataLayout) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert(dataLayout instanceof DataLayout, 'dataLayout must be a DataLayout');
-    assert.strictEqual(typeof callback, 'function');
-
-    callback(null);
 }
 
 function upload(apiConfig, backupFilePath, sourceStream, callback) {