diff --git a/ogclient/interfaceAdm/Configurar.py b/ogclient/interfaceAdm/Configurar.py
index ac94750..7934ce1 100755
--- a/ogclient/interfaceAdm/Configurar.py
+++ b/ogclient/interfaceAdm/Configurar.py
@@ -78,6 +78,8 @@ tbf = {}  # Tabla de formateo
 sparams = sparam.split('%')
 
 maxp=0
+sum_tam = 0
+do_sum_tam = True
 for item in sparams:
     if not item: continue         ## por si nos pasan un '%' al final de todo
         # Leer datos de la partición, separados por "*".
@@ -94,7 +96,7 @@ for item in sparams:
         if   'par' == k: par = int (v)
         elif 'cpt' == k: cpt = v
         elif 'sfi' == k: sfi = v
-        elif 'tam' == k: tam = v
+        elif 'tam' == k: tam = int (v)
         elif 'ope' == k: ope = int (v)
 
     missing_params = []
@@ -111,6 +113,11 @@ for item in sparams:
         tch = tam
     else:
         tbp.append (f'{cpt}:{tam}')
+        if do_sum_tam:
+            sum_tam += tam
+        if 'EXTENDED' == cpt:
+            do_sum_tam = False      ## don't sum sizes anymore
+
     if ope:
         # Si se activa operación de formatear, componer datos de formateo.
         if cpt not in ['EMPTY', 'EXTENDED', 'LINUX-LVM', 'LVM', 'ZPOOL']:
@@ -119,7 +126,10 @@ for item in sparams:
     if par > maxp: maxp = par
 
 if tch is None:
-    tch = '0'
+    tch = 0
+
+if is_there_cache and 0 == tch:
+    print (f'nati ===================== is_there_cache ({is_there_cache}) tch ({tch}), this should not happen')
 
 
 
@@ -133,6 +143,29 @@ if cur_ptt and ptt != cur_ptt:
     SystemLib.ogEcho (['session', 'log'], None, f'Current partition table type "{cur_ptt}" is wrong for this system--will replace it for a "{ptt}" one')
     recreate_partition_table = True
 
+
+## size check: check that cache fits in the space left by the previously existing partitions
+if not recreate_partition_table and not CacheLib.ogCheckNewCacheSize (dis, tch):
+    SystemLib.ogRaiseError (['log', 'session'], ogGlobals.OG_ERR_CACHE, f'nueva partición de caché no cabe en el hueco actual')
+    sys.exit (1)
+
+## size check: check that the newly defined partitions fit in the space left by the newly defined cache
+disk_sectors = DiskLib.ogGetLastSector (dis)
+IOSIZE = 512  ## TODO
+if 512 == IOSIZE:
+    sum_tam_sectors = sum_tam*2
+    cache_sectors = tch*2
+else:
+    sum_tam_sectors = (sum_tam+3)//4    ## sumamos 3 para que la división entera "redondee al alza"
+    cache_sectors = (tch+3)//4
+## esta comprobacion puede dejar pasar situaciones que más tarde dan error
+## la ventana es bastante estrecha, y sumando aquí simplemente un 1 por 1000, ya la cerramos del todo
+sum_tam_sectors = int (sum_tam_sectors * 1.001)
+space_left_by_cache = disk_sectors - cache_sectors
+if sum_tam_sectors > space_left_by_cache:
+    SystemLib.ogRaiseError (['log', 'session'], ogGlobals.OG_ERR_CACHE, f'las particiones no caben en el disco')
+    sys.exit (1)
+
 #____________________________________________________
 #
 # Proceso
diff --git a/ogclient/lib/python3/CacheLib.py b/ogclient/lib/python3/CacheLib.py
index 28ad37b..a7bf170 100644
--- a/ogclient/lib/python3/CacheLib.py
+++ b/ogclient/lib/python3/CacheLib.py
@@ -364,3 +364,40 @@ def ogUnmountCache():
 def initCache (*args):
     p = subprocess.run ([f'{ogGlobals.OGSCRIPTS}/initCache.py'] + list(args))
     return not p.returncode       ## negate shell return code
+
+
+#/**
+#         ogCheckNewCacheSize
+#@brief   Comprueba si un cache de X tamaño cabe en el hueco que dejan las demás particiones
+#@param   Tamaño de la nueva hipotética cache
+#@return  Boolean, True si la nueva cache cabría, False si no
+#*/ ##
+def ogCheckNewCacheSize (disk, kB):
+    IOSIZE=512 #DiskLib.blablaIoSize (disk)
+    last_sector = DiskLib.ogGetLastSector (disk)
+
+    end_of_last_partition = 0
+    cachepart = ogFindCache()
+    if cachepart:
+        cache_disk, cache_part = cachepart.split()
+        cache_dev = DiskLib.ogDiskToDev (cache_disk, cache_part)
+    else:
+        cache_dev = None
+    fdisk_l_out = subprocess.run (['fdisk', '-l'], capture_output=True, text=True).stdout
+    for l in fdisk_l_out.splitlines():
+        if not re.match ('^/dev', l):                     ## no empieza por /dev, nos la saltamos
+            continue
+        if cache_dev and re.match (f'^{cache_dev}', l):   ## es la de cache, nos la saltamos
+            continue
+        last_sector_of_partition = int (l.split()[2])
+        if last_sector_of_partition > end_of_last_partition:
+            end_of_last_partition = last_sector_of_partition
+
+    if 512 == IOSIZE:
+        cache_sectors = kB*2
+    else:   ## 4096
+        cache_sectors = (kB+3)//4    ## sumamos 3 para que la división entera "redondee al alza"
+    if end_of_last_partition + cache_sectors > last_sector:
+         SystemLib.ogEcho (['session', 'log'], None, f'end_of_last_partition ({end_of_last_partition}) + cache_sectors ({cache_sectors}) > last_sector ({last_sector}), check failed')
+         return False
+    return True